The present invention relates to the field of graphic arts. More particularly, it relates to an improved photographic contact printing system in which the task of achieving a desired exposure of a photosensitive recording element is greatly simplified.
In the field of graphic arts, it is common to use a contact printing process to produce images, such as half-tone and line-art images, on photographic films and papers. In such a process, an original document, usually in the form of a transparency, is contiguously arranged with respect to a sheet of photosensitive material, typically a photographic film. The latter is exposed through the original to produce a developable image of the original on the photosensitive sheet. In achieving a desired image density on the photosensitive sheet, several variables come into play. They include, of course, the speed and spectral characteristics of the photosensitive recording element, as well as the spectral radiance of the light source which, in the case of conventional metal-halide and tungsten-filament lamps, varies dramatically with time. Also important in the production of half-tone and line-art images are the dot-growth and overlay factors of the recording media. As is well known, different films and papers (and there are many) have considerably different characteristics which affect the exposure they require and the results they provide.
In determining the proper exposure for a particular recording medium, it is common for the graphic artist to run a series of experiments in which a film strip is exposed at several different exposure times. Upon processing the film, the artist determines from the various density levels of the developed image, which exposure time is best suited to achieve the desired results. Usually, the optimum exposure requires an interpolation process in which the artist estimates the optimum exposure time from two images which straddle the the desired density level. Each time a different film is used, this experimental process of determining optimum exposure time is repeated, ad nauseam.